The present invention relates to a rapper device for cleaning heat exchange surfaces in a pressure vessel for transporting hot dust-laden gas.
Hot process gases can contain fouling components, such as fine dust and molten or evaporated components, which turn sticky when they cool and condense, thereby adhering to each other and to surfaces in contact with the gases. These fouling components can form harmful deposits, particularly on heat exchange surfaces.
Such hot process gases can for example be synthetic gases synthesized by partial combustion processes, generally referred to as syngas. These gases are guided along heat exchanging surfaces in a pressure vessel.
Fouling deposits from hot dust laden process gases can be removed by using a rapper device, such as the rapper device disclosed in British patent application GB 2 104 614 A. This prior art rapper device comprises an energy transmitting element or striker having one end within a pressure vessel contacting the heat exchange surface to be cleaned, and one end outside the pressure vessel, which is repetitively knocked by an impact device. The impact energy of the knocking device is passed through the energy transmitting element to the heat exchange surface. The heat exchange surface and the deposits adhering thereto are accelerated differently by the transmitted impact energy as a result of different mass moments of inertia. As a result, the deposits fall off the heating surface.
The pressure within the pressure vessel is much higher than the atmospheric environmental pressure outside the pressure vessel. For example, in coal pressure gasification plants the pressure in the heat exchange vessel can be as high as about 40 bar. Due to these differences in pressure, the energy transmitting element or striker is forced towards the outside of the pressure vessel. In GB 2 104 614 A, a gas pressure equalizing device is used to overcome this force. Since the pressure on the one end of the striker should be equal to the pressure exerted on the end abutting the heat exchange surface, the surface area of the energy transmitting element within the pressure chamber should be sufficiently high. Since in GB 2 104 614 A the wall of the pressure vessel is interrupted where it is passed by the striker, a number of seals must be used to prevent leakage of synthetic gas, which is toxic and inflammable. These seals typically have short life cycles.
The striker is subjected to repetitive impact loads. This results in the formation of cracks after a number of operation cycles, particularly at locations of abrupt diameter changes. This limits the technical life time of the device.